Curved electrode or flexing beam microelectromechanical systems (MEMS) actuators have been fabricated and tested for applications including optical beam and electrical switching. During operation, in response to an actuation voltage, the beam flexes to conform to the shape of the stationary electrode. These curved electrode actuators are typically classified as either out-of-plane or in-plane devices. This taxonomy is based on how the beam moves relative to the plane of the substrate.
Generally, out-of-plane devices are most common. One example is sometimes referred to as the rollershade actuator. A beam structure is fabricated on a substrate. Residual material stress in the beam structure is cultured such that the top of the beam is under compressive stress and the bottom is under tensile stress. Thus, when released from the substrate, the beam tends to curl-up. This tendency is counterbalanced by modulating a voltage between the curled beam and the substrate. The resulting electrostatic forces are used to unroll the rollershade beam so that it conforms to the flat substrate electrode.
Display devices based on two-dimensional arrays of rollershade switches have been proposed. In another application, the rollershade switches are diced into individual devices or linear arrays to function as beam switches in free-space interconnects for fiber optic systems.
In-plane devices are sometimes referred to as zipper actuators. Here, the beam flexes or moves predominantly in a direction that is parallel to the plane of the substrate. R. Legtenberg, et al., in an article entitled Electrostatic Curved Electrode Actuators, from Journal of Micro-Electro-Mechanical Systems, Vol. 6, No. 3, September 1999, characterized the behavior of zipper actuators. The paper presented design and performance information for an electrostatic actuator consisting of a laterally compliant cantilever beam and a fixed, curved electrode, which were both suspended above a ground plane. Suggested applications for these actuators included bi-stable applications, namely microswitches, microgrippers, microvalves, and micropumps.
The present invention is directed to the use of zipper actuators for optical beam control. Specifically, the invention is directed to a number of innovations to enable the zipper actuators to function as optical beam shutters and/or beam switches in free space interconnect optical systems, for example.
In general, according to one aspect, the invention features a micro-optical electromechanical system. Such systems are characterized by semiconductor-style wafer processing techniques including deep reactive ion etching, for example, and/or small size in which the optical beams are less than a few millimeters in diameter.
The inventive system comprises a substrate with an optical port. A stationary electrode is provided on substrate, along with a cantilevered beam extending from the substrate. The stationary electrode and the cantilevered beam are oriented such that an electrical field between the stationary electrode and the cantilevered beam causes the cantilevered beam to pivot toward the stationary electrode, in a plane of the substrate.
In the present implementation, a face of the stationary electrode adjacent the cantilevered beam is arcuate. In other implementations, the stationary electrode is semi-circular or circular. In still other embodiments, the stationary electrode can be straight or near straight with a straight or curved beam. During operation, in response to an electrical field, the cantilevered beam flexes toward the stationary electrode.
The optical port is preferably located relative to the cantilevered beam such that the pivoting causes the cantilevered beam to intercept an optical signal that is directed to pass through the optical port. In one implementation, the cantilevered beam acts as a shutter and/or mirror that modulates the magnitude of an optical signal transmitted through the optical port.
In general, according to another aspect, the invention again features a micro-optical electromechanical system. This system comprises a substrate and a stationary electrode on the substrate. A cantilevered beam extends from the substrate such that an electrical field between the stationary electrode and the cantilevered beam causes the cantilevered beam to pivot toward the stationary electrode in the plane of the substrate. Finally, the cantilevered beam includes a paddle for interacting with or switching an optical signal.
In the typical implementation, this paddle is simply a widened portion of the cantilevered beam. This allows the cantilevered beam to be relatively thin, and therefore flexible, to thereby reduce the required actuation voltages. In the present example, the paddle extends parallel to a plane of the substrate.
Of course, in alternative implementations, the paddle can project in a direction that is vertical or substantially vertical to a plane of the substrate. Typically, in this second example, the paddle is installed on the cantilevered beam in an assembly step, because of the difficulty of monolithically forming such a vertical structure.
In one implementation, the optical port region comprises an anti-reflection coated region of the substrate. Alternatively, the optical port region can be a hole that is formed at least partially, or completely, through the substrate. This minimizes the insertion loss associated with the system by avoiding absorption and/or reflection at the substrate. In the preferred implementation, the paddle comprises a mirror structure for reflecting an optical signal. This allows the system to switch an optical signal that is being directed through the port either back toward the source or at an angle relative to the source.
In general, according to another aspect, the invention features a micro-optical mechanical system. This system comprises a substrate having an optical port formed through the substrate and a stationary electrode on the substrate. A curved cantilevered beam extends from the substrate and wraps around the stationary electrode in a relaxed state. Electrical field between the stationary electrode and the cantilevered beam causes the cantilevered beam to curl around the stationary electrode in the plane of the substrate. This curved beam implementation is useful in applications that require more compact structure than versions with a straighter cantilevered beam.
Generally, according to still another aspect, the invention features a cantilevered beam micro-optical electromechanical system. This aspect of the invention includes a latch for holding the cantilevered beam in a fixed location relative to the substrate.
In one example, the latch is implemented as a hold-down electrode that draws the cantilevered beam to an adjacent structure, such as the substrate. Alternatively, MEMS-style latch systems can be used, such as a pawl system that locks the cantilevered beam in a stationary position, such as covering the optical port or in a position where it does not obstruct the optical port.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.